The Nurses' Health Study (NHS) is an ongoing epidemiologic study of 121,700 female U.S. registered nurses, aged 30-55 years in 1976. The NHS is the largest population-based cohort used for rheumatic disease epidemiology and has been used to test hypotheses in systemic rheumatic conditions such as RA and SLE. Osteoarthritis (OA) has not been studied in this cohort because of the expense and the difficulties inherent in its case definition. The present proposal is to conduct a study of the validity of a self-reported diagnosis of knee OA and hip OA among a subset of women from the NHS, allowing us to demonstrate the feasibility of a large scale study of dietary and hormonal predictors of self- reported OA in the NHS.